The Evolutionary Psychology FAQ

Edward H. Hagen, Institute for Theoretical Biology, Berlin

Are there enough genes to build psychological adaptations?

"People don't have enough genes to program all the behaviors some evolutionary psychologists, for example, believe that genes control."

"Evolutionary psychology is dead but doesn't seem to know it yet."

Paul Ehrlich, presumably referring to the announcement that the human genome contains only 30,000 genes (an estimate that is in flux)
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Some critics of evolutionary psychology claim that there simply arenít enough genes to code for a large number of innate cognitive adaptations (Ehrlich and Feldman 2003). Curiously, they donít suggest that there arenít enough genes to build the thousands of anatomical adaptations that have already been discovered, they havenít suggested the theory of natural selection is wrong, nor have they called for an immediate halt to the billions of dollars of research aimed at furthering the functional understanding of cells, tissues and organs, research that, if the critics were right, would be useless given that there arenít enough genes to build all those adaptations. Current estimates are that humans have 20,000-60,000 genes. If genes and adaptations corresponded in a one-to-one fashion, then, if it took an average of 100 genes to code for an adaptation, there could only be 200-600 adaptations, a number we have already long surpassed in our investigation of anatomy and physiology.

Adaptations, however, are not the simple product of genes. Rather, they are the product of gene interactions. Although the processes by which genetic information directs the development of cells, tissues, and organs are still largely unknown, it is well known that both genes and non-gene regions of DNA control the protein production of other genes, and that multiple proteins combine to produce an adaptation. These simple facts fundamentally alter the math. Imagine an organism with four genes, A, B, C, and D. In the naÔve view, this organism could have at most four adaptations, one coded for by each gene. But if genes interact, then this organism could have as many as fifteen adaptationsónot only those produced by A, B, C, and D, but also those produced by all possible combinations of A, B, C, and D (AB, AC, AD, ABC, ABCD, BC, BD, etc.). For an organism with Ďonlyí 30,000 genes, the number of gene combinations explodes. The total number of two-gene combinations, for example, is almost half a billion. To produce an adaptation, however, often many more than two genes interact. The total number of 25-gene combinations is around 1086 (in comparison, the universe probably contains around 1080 particles). An organism obviously need make use of only a minute fraction of such gene combinations to produce an incredibly rich, functionally organized phenotype with enormous numbers of adaptations. (Some have claimed that gene interactions are themselves an impediment to the evolution of adaptations. Although this can be true over the short-term, it isnít over the long term, e.g., Hammerstein, P. 1996. Darwinian adaptation, population genetics and the streetcar theory of evolution. J. Math. Biol. 34: 511-532).

Copyright 1999-2002 Edward H. Hagen